Medical care of persons with Down's has improved in recent years

Dr Sonja Rasmussen

About one in every 800 people is born with Down's syndrome, a genetic condition caused by the presence of an extra chromosome.

However, although it is relatively common, information about illness and the causes of death in people with Down's syndrome is limited.

A team from the Centers for Disease Control and Prevention in Atlanta examined death certificates of around 17,900 people with Down's who died between 1983 and 1997.

They found that over that time the average age at death increased from 25 to 49 years.

People from non-white races were more likely to die younger than white people with Down's syndrome.

People with Down's were more likely to die from conditions such as congenital heart defects, dementia and leukaemia.

However, with the exception of leukaemia and testicular cancer, other types of cancer were listed on death certificates less than one-tenth as often as expected.

Several theories

The reason for this is unclear, but it is possible that the extra chromosome associated with Down's contains genes that act to suppress the development of tumours.

The chromosome - number 21 - is known to play an important part in the immune system.

Alternatively, it could be that Down's syndrome cells may reproduce themselves more slowly, giving less opportunity for replication errors in genes involved in tumour formation.

A third possibility is that people with Down's syndrome are exposed less often to environmental agents that stimulate cancer.

Researcher Dr Sonja Rasmussen, a clinical geneticist, told BBC News Online there were several possible reasons why life expectancy has increased.

She said: "Previously, persons with Down syndrome may have been institutionalised.

"Today most children with Down's live with their families, and older persons with Down's often live in group homes or other facilities in the community.

"Medical care, especially treatment of congenital heart defects among persons with Down's, has also improved in recent years."

Sixty plus

A spokesperson for the Down's Syndrome Association said the research confirmed the charity's own experience.

"The outlook for people with Down's syndrome is much rosier than in the relatively recent past with many born today probably able to look forward to a healthy life of sixty years plus."

She agreed that treatments for certain life threatening conditions that are more common in people with Down's syndrome - such as heart defects and leukaemia - had improved significantly.

However, she added: "Difficulty in getting access to appropriate healthcare is still a reality for many and more must be done to improve training and information for medical students and professional health care workers."